Go here for Searle's review of Chalmer's book (The Conscious Mind: In Search of a Fundamental Theory).
Here is the review at Psyche.
A perspectives article on Chalmers, other philosophers of mind, and dualism.
Review by Max Velmans

It was enough for me to just read David Chalmers' article "The Puzzle of Conscious Experience" in Scientific American. December 1995, pages 80-86.

Chalmers is a dualist. Human kind has grown up with dualism, we are all naturally dualists: the mechanistic basis of our thoughts is invisible to our introspection and casual powers of observation. Even now that objective scientific investigation of the human brain has allowed us to understand that mind is just a functional consequence of complex brain activity, even now dualism remains a persistent meme. Chalmers is not alone in his dualism, but he is innovative in trying to construct a modern form of dualism upon which a modern career in philosophy can be built.

David Chalmers' version of dualism is audacious and amusing. He does not claim that there is a simple mind/brain dualism. Chalmers has to admit that neuroscience is able to explain many aspects of the mind in terms of brain activity. Chalmers divides both mind and brain activity into two categories: 1) brain activities and aspects of the mind that have a clear functional role in behavior, and 2) brain activities and aspects of the mind that Chalmers imagines could be dispensed with and not cause any change in behavior since all they do is provide us with our subjective experience of events. Chalmers says that the first kind of aspects of mind can be more easily explained by the investigations of neuroscientists and other investigators of the brain. In contrast, the second kind of aspects of mind are tricky: "Subjective experiences seem to emerge from physical processes, but we have no idea how or why." Platonic essentialism is Chalmers' dualistic game: subjective experience is "sparkling" and "ineffable" while "how a human subject discriminates sensory stimuli and reacts appropriately" is essentially different, and explainable in terms of crass physical brain processes.

This is an audacious surgical splitting of the both mind and brain into two essentially different parts. If we accept Chalmers' claim that his is the proper way to approach the problem of mind then we can follow him on a wild and mysterious ride, a ride likely to be long enough to sustain a modern career in philosophy. But what if we do not accept Chalmers' assumption that this is a reasonable way to approach the problem? How should we decide the question of whether the mind actually adheres to Chalmers' dualistic classification scheme?

To start our evaluation of Chalmers' approach to the mind, we can compare it to that of other investigators of the mind. According to Chalmers, introspection is a corner stone of the study of mind: " For a start, each one of us has access to our own experiences." Clearly, the human brain, the sole source of our subjective theater of experience, does not have any direct means of learning about the material basis of its own activity. In short, subjective experience sucks as a source of reliable knowledge about the brain.

What else does Chalmers rely upon for insight into mind? "Philosophical arguments and thought experiments also have a role to play." Gee, such an arsenal. I supose it warms Chalmers' heart to imagine a long career unfolding before him during which these rapier investigative tools will have no chance of solving the mystery of mind.

Compare Chalmers' approach to that of neuroscientists like Francis Crick and Christof Koch who propose to, "Concentrate on the processes in the brain that are most directly responsible for consciousness." I am on their side: experimental investigation of the brain is what we need. It is astounding that anyone even vaguely familiar with the history of science could still fail to see the comparative sterility of introspection and philosophizing as compared to objective experimental investigation.

It is introspection and philosophizing that has never had to confront the cold test of experiment that is the basis of Chalmers dualistic division of mind into subjective experience and everything else. Chalmers can imagine that conscious experience is nothing but a dispensable epiphenomenon of the brain activity that could just as efficiently control behavior in the complete absence of subjective sensations. Hey, if introspection and thought experiments brought us to this approach to mind, surely introspection and thought experiments can bring us to the complete solution of this hard problem.

Unfortunately, most biologists have a different approach to mind. Biologists find it easy to suppose that subjective conscious experiences are themselves functionally relevant, having been selected by natural selection for their survival value.

In discussing the crass mechanical functioning of brains Chalmers claims, "Nobody knows why these physical processes are accompanied by conscious experiences at all." Is this really the great mystery that Chalmers makes it out to be? Chalmers sounds like the thousands of philosophers, their asses firmly held to the ground by gravity, who have gazed up in the sky at the planets and smugly concluded, "Nobody will ever know what mysterious force guides the planets through the sky." Chalmers is so convinced that explanations of subjective experience are inherently mysterious that he refuses to make the Newtonian leap of imagination.

The solution to the mind/brain mystery may not be as obvious as the force that holds Chalmers in his chair, but there is much experimental evidence that tells us that conscious experience is functionally relevant for our behavior, not some mysterious epiphenomenon. We have several powerful methods that cause alterations subjective experience and allow us to observe how behavior is altered at the same time. Brain damage can cause dramatic changes in subjective experience. Chalmers uses the experience of perceiving colors as an example of the mysteries of subjective experience. Some people suffer strokes which cause destruction of just those parts of the visual cortex that are needed for perception of color. Such a brain defect not only destroys the ability to subjectively experience colors, but also prevents these people from performing useful behaviors related to color discrimination. Clearly, primates have evolved to make use of subjective experience of color as part of our ability to respond successfully to colors in the environment. There is a huge over-lap in the brain cells that provide for our subjective awareness of color and our ability to respond constructively based on colors in our environment. Chalmers may be able to imagine brains in which subjective experience of colors is a dispensable epiphenomenon, but evolution made color perception and our subjective experience of color inseparable aspects of the same brain activity. Is this any more mysterious than the strange fact that Newton found a single explanation for a falling apple and the orbit of the moon? I think not.

Another way to show that subjective experiences are not epiphenomena is by using drugs to alter brain function. Most of us have observed the ability of drugs to alter behavior and subjective experiences. Many drugs effect specific neurotransmitter receptors in the brain. The same brain parts that control our subjective awareness control our behavior. Where is the experimental evidence to support Chalmers' claim that subjective experiences are mysterious epiphenomena? Clearly, our brains make use of subjective experiences as part of our mechanism for controlling behavior. The rational observer can expect that any mystery in this strange situation will evaporate as we learn the details of how our brains function.

A few neuroscientists like Antonio Damasio have taken on the challenge of learning how emotion and feelings are integrated into the human capacity for planning and executing complex adaptive behaviors. There is certainly good reason to agree with Chalmers that issues like subjective experience are the hard part of neuroscience. Most neurobiologists (like Crick and Koch) purposefully try to ignore the less experimentally accessible aspects of consciousness, preferring instead to first deal with the easy problems. Subjective experience is a poor choice for investigation when so much can be learned about the control of visual awareness in experimental animals without the need to ask them about their subjective experiences. Is there any reason to believe that there might be a domino effect: if we solve the easy problems of consciousness first will the harder aspects of consciousness then become easier to solve?

We have many reasons to hold this optimistic view. Chalmers points out the fact that conscious experiences are involved in how small sub regions of the brain make local information available to other, distant parts of the brain. Crick's book, "The Astonishing Hypothesis", examines possible brain mechanism that might solve to the binding problem in visual awareness: how many individual sets of information derived in the many functional sub regions of visual cortex are coordinated with each other. For example, Crick discusses experiments with monkeys in which experimental modulation of neuronal activity in the visual cortex alters the animals' visual perception. It is not a great leap of faith to suspect that if these experiments were done on Chalmers, he would report concomitant changes in his subjective experiences. Some people have had electrodes implanted in their brains: stimulation of neurons can clearly cause subjective experiences. The mechanistic basis of subjective experiences may be relatively inaccessible, but we have no reason to view them as fundamentally mysterious.

The fact that I can not share your personal subjective experiences does not imply that I can not understand the basic mechanisms by which your brain produces your experiences. I see the brain mechanisms of memory as key processes underlying consciousness. Neuroscience is now revealing the molecular and cellular mechanisms of memory. In another 10 or 20 years we will be able to present Chalmers with a theory of how brain memory processes construct subjective experiences. Newton constructed his theory of gravitation based on a few simple measurements and calculations. The brain is vastly more complex, but we have no need to suspect incredibly deep mysteries. If we roll up our sleeves and keep our young students of the mind busy in neuroscience labs studying the brain, we may even be able to send Chalmers into an early retirement. And we won't even have to rely upon physicists finding "experience" as a fundamental property of the universe, just a fancy tool brains have evolved for getting the next meal. Gee, maybe that's where Chalmers got the idea of making a career out of the philosophy of subjective experience.

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